Mineralization of Gold Nanoparticles in a Block Copolymer Microemulsion

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Abstract
Controlled mineralization of gold nanoparticles has been performed in a microemulsion of polystyrene‐block‐poly(2‐vinylpyridine). The starting point was the formation of a thermodynamically stable dispersion of HAuCl4 in inverse micelles of the block copolymer in toluene, which became metastable when the gold was reduced. Kinetic control of the transformation allowed the following stages of the mineralization/coagulation process to be stabilized: 1) one gold particle per micelle, 2) aggregated micelles containing two or three gold particles, and 3) a state in which empty micelles coexist with larger polymer‐stabilized gold particles. Distinctive variations in the spectra were observed depending on the particle size and whether two particles had formed a couple with orientation‐dependent dipolar interactions.